Google Cloud Console shows Client is unauthorized to retrieve access tokens using this method in python

I saw so many question relating to this GCP issue, none of it helped. I have created service account and added to "Manage Domain-wide delegation" with scopes. But I still get this error Client is unauthorized to retrieve access tokens using this method or client not authorized for any of the scopes requested.

code is below:

from google.oauth2 import service_account


SCOPES = [
    "https://www.googleapis.com/auth/admin.directory.user",
    "https://www.googleapis.com/auth/admin.directory.domain.readonly",
    "https://www.googleapis.com/auth/gmail.readonly",
    "https://www.googleapis.com/auth/gmail.send",
    "https://www.googleapis.com/auth/gmail.insert",
    "https://www.googleapis.com/auth/gmail.settings.sharing",

]

SERVICE_ACCOUNT_FILE = '/PATH/TO/FILE/credentials.json'
credentials = service_account.Credentials.from_service_account_file(
        SERVICE_ACCOUNT_FILE, scopes=SCOPES, )
delegated_credentials = credentials.with_subject('email')
service = build('admin', 'directory_v1', credentials=delegated_credentials)

def main():
    print("Getting the first 10 users in the domain")
    results = (
        service.users()
        .list(customer="customer_id", maxResults=10, orderBy="email")
        .execute()
    )
    users = results.get("users", [])
    print(users)

Delegation means impersonating another identity. What permissions does the identity in this line of code have credentials.with_subject('email')? The identity needs super administrator access to the relevant Google Workspace account.

Additionally, the user must have logged in at least once and accepted the Google Workspace Terms of Service.